The invention relates to “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European Communities, specifically implants to continuously monitor heart rhythm and deliver if necessary to the heart electrical pulses for stimulation, resynchronization and/or defibrillation in case of rhythm disorder detected by the device.
Bradycardia pacing involves the controlled delivery of pulses to the atrium and/or to the ventricle (simple or dual chamber devices). In the case of cardiac resynchronization therapy (CRT), stimulation must also be applied in conjunction to the two ventricles (multisite device).
The invention relates more particularly to the detection of “anodic stimulation,” which is characterized by a reversal of the cathode and the anode during stimulation, resulting in that the stimulation is not delivered in the required manner and that the depolarization wave induced by this improper stimulation is not as expected, with all the adverse effects that may result.
Certain conditions favor the occurrence of this phenomenon, in particular:                Relatively high stimulation amplitudes, nevertheless close to the stimulation threshold; and        An “intercavity stimulation vector” configuration, that is to say, a configuration in which a stimulus is applied in a given cavity (for example the left ventricle) with the anode in a lead implanted in the opposite cavity (for example an electrode of a right ventricular lead).        
These conditions typically occur during the execution of a “capture test,” which is a test of determining whether stimulation was effective or not by research and analysis of the “evoked wave,” that is to say of the depolarization wave induced by stimulation of a cavity. This test should be performed at regular intervals, and can also be made permanently, cycle to cycle. It is intended to regularly adjust the amplitude and/or the width of the stimulation pulses, that is to say, the energy delivered to the stimulation site, depending on the myocardium response to these pulses.
In some cases, detection of the pacing threshold must be made indirectly, with a detection within a cavity which is different than that which is stimulated, for example by stimulation of the sole left ventricle and detection of signals collected in the right ventricle. In such a situation, the cycles with anodic stimulation must be excluded from the analysis of the signal, because they are not representative and therefore cannot be properly discriminated in capturing cycles or non-capturing cycles.
Anodal stimulation also produces deleterious effects in patients undergoing a cardiac resynchronization therapy (CRT), in which a non-zero delay between the two ventricular stimulations (interventricular delay or VVD) is implemented and adjusted to optimize the hemodynamic response of the patient. Under these conditions, anodic stimulation is characterized for example by stimulation of the left ventricle causing a concomitant contraction of the right ventricle, resulting in loss of the VVD. This phenomenon is not uncommon in patients undergoing biventricular pacing; it can be detected and the device may take appropriate measures, such as changing the pacing configuration with switching to another stimulation vector with which there is no anodic stimulation (such as a bipolar vector, an unipolar vector or another interventricular vector by selection of other electrodes of the lead).
Various techniques have been proposed to detect the emergence or presence of an anodic stimulation, for example, as described in U.S. 2009/0030470 A1, U.S. 2010/0262204 A1, U.S. 2008/0071318 A1, U.S. Pat. No. 6,687,545 B1 or WO 2012/071331 A2.
These known detection methods are generally based on the observation that if a stimulus in a given cavity causes an immediate depolarization in the opposite cavity, this reveals the presence of an anodic stimulation, while a late depolarization in this opposite cavity indicates the absence of anodal stimulation.
With these known techniques, the detection is based on the analysis of a single endocardial electrogram signal (EGM signal), which has the disadvantage that the detection entirely depends on the quality of that EGM, which can sometimes be compromised.